The present invention relates to a sequence switching system in a tracer control unit with which it is possible to manually change the timing for switching of a tracing sequence by means of a control switch externally provided.
Conventional tracer control units, in general, mechanically set a tracing path, for example, a tracing range in the X-Y plane by means of a limit switch, or by storing the machine position in a memory, and cut a workpiece within the set range while at the same time tracing a model with a stylus of the tracer head. It is difficult, however, to accurately predetermine the tracing range. To get over this problem, a sequence changeover system has heretofore been proposed which has a control switch externally provided for manually changing the switching of a tracing sequence, and which permits, by pressing the control switch, a sequence changeover, for instance, from a tracing operation to a pick feed operation even if the stylus lies within a preset tracing range. According to such a sequence, changeover system, a desired tracing range is first set and then modified in succession during the actual tracing operation.
With the conventional sequence changeover system, however, the sequence changeover is possible only within the preset tracing range but impossible outside it. This inevitably calls for a wide preset tracing range, incurring an increase in the time for tracing.